Relationship of a cerebral autoregulatory index with outcome in head injured patients

Background Cerebral autoregulation is the process by which cerebral blood flow (CBF) is maintained constant over a specific cerebral perfusion pressure (CPP) range. We have reworked a version of the Ursino and Lodi autoregulation model to derive an index of autoregulation (G), and compared it to a number of other autoregulatory models as well as a gold standard measure of autoregulation obtained from an animal model study (6 piglets with a cranial window preparation and ICP, ABP sampled at 250 Hz). The results of that study have shown that this index G correlates well with the “Bouma” index of autoregulation.

Methods In this study this new autoregulatory index has been calculated for a sample of 12 head injury patient's data over multiple time points and then used to firstly investigate if this index in conjunction with other clinical prognostic factors may give a better indication of outcome and then analyse its trend with time to quantify how the level of autoregulation changes post-injury.

Findings The index correlates well with dichotomised GOSe outcome (p=0.03) and the trend in the result between middle and late time periods shows early signs of being predictive of outcome as well.

Conclusions Though more work is needed these results warrant further investigation with larger numbers of patients